ISLAMABAD, Pakistan | Pakistan seized three bomb-laden vehicles and arrested three suspected suicide attackers, uncovering a terror plot just days after an assault on the Danish Embassy, officials said Friday.

Authorities ramped up security near the enclave where most foreign diplomatic missions are located. The U.S. Embassy strongly advised Americans to limit nonessential movement in the capital and nearby Rawalpindi.

An Internet posting Thursday, purportedly from al Qaeda in Afghanistan, claimed responsibility for Monday’s bombing outside the Danish Embassy in Islamabad that killed six persons, including one Dane.

The group threatened more attacks on countries where caricatures of prophet Muhammad are published. The images carried in various Danish and other Western newspapers over the past three years have sparked periodic unrest in the Muslim world.

Police and intelligence agents late Thursday arrested about six suspects, including three suicide bombers, in Rawalpindi, about seven miles from Islamabad, officials said.

The authorities seized three vehicles laden with more than 2,200 pounds of explosives, Rawalpindi police said.

Mr. Durrani said the arrested men were Pakistanis and their targets included an office in Rawalpindi of President Pervez Musharraf, a longtime U.S. ally in its war on terror. Pakistan’s army also has its headquarters in the city.

Sweden, whose embassy is near the Danish mission, said it had increased security in response to the arrests.

Pakistani officials said Monday’s attack on the Danish Embassy was carried out by a suicide attacker in a car equipped with fake diplomatic registration plates.

The attack is likely to add to Western unease over peace talks with militants launched by Pakistan’s new government in hopes of curbing Islamic extremist violence.

The U.S. is worried the deals will give militants time and space to regroup in Pakistan’s tribal regions, where Taliban and al Qaeda are believed to find sanctuary.

On Friday, Pakistan’s Foreign Minister Shah Mehmood Qureshi visited Afghanistan, which fears an escalation in Taliban attacks on its side of the border. He reiterated the government’s assertion it will not cut deals with terrorists.